A Novel Demodulation Method for Fabry-Perot Sensors in Ultrasonic Partial Discharge Detection

Fabry-Perot (F-P) optical fiber sensors have gained significant attention in ultrasonic partial discharge (PD)detection for power equipment due to their electromagnetic interference immunity and intrinsic safety. Conventional intensity demodulation methods suffer from operating point sensitivity, where oil temperature variations alter the probe cavity length, leading to operating point drift and output instability. To address this limitation, a novel heterodyne interferometry-based demodulation system for F-P sensors is proposed, which eliminates dependence on optical intensity and operating point, ensuring stable signal output. The ultrasonic sensor detection platform was established to compare the detection performance of the new heterodyne interference demodulation method with the traditional intensity modulation system. The experimental results indicate that the heterodyne interference system exhibits a higher signal-to-noise ratio (SNR), with a 4.5 dB improvement in SNR over the intensity modulation method in the 20 kHz to 80 kHz frequency range. Furthermore, partial discharge tests on the standard sphere-plane electrode model showed 5.4 dB SNR enhancement in the heterodyne demodulation topology compared with intensity-based approaches. The comprehensive experimental verification confirms that the proposed heterodyne interferometric demodulation system represents a stable-response demodulation approach for partial discharge detection.